Hi Mel
Thanks for your query – great to hear that RORB is being used in NZ!
For Australian conditions an m value of 0.8 is usually recommended, however this can be changed where there is sufficient evidence to warrant it (such as calibration to gauged streamflow hydrographs). Section 2.2.1 of the RORB Manual suggests that 0.6 is the lower bound of likely m values.
The other thing to consider is interaction between the m and kc values. In Australia there are various regional equations which can be used to check that a calibrated kc value is within a suitable range. The most common of these is the paper titled “A Simple Method for Estimating RORB Model Parameters for Ungauged Rural Catchments” by Mark Pearse, Phillip Jordan and Yvette Collins (http://search.informit.com.au/documentSummary;dn=316886237612094;res=IELENG). This suggests that the value of kc should be between about 0.6 and 2.1 times the value of the average flow distance (dav, which is summarised for you in the kc selection dialogue box) for the catchment. This might be a useful check, although it is based on Australian data only.
Assuming that you are confident in the results of the model calibration and that the kc value is within a reasonable range, it should be OK to proceed to design runs using an m value of 0.8.
Hope this helps.
